Steering moving craft



Nov. 22, 1938. E. E. LIBMAN 2,137,847

STEERING MOVING CRAFT Filed May 16, 1936 g5 Figi /voRrH n F521' MA ENE7' IC BEAR/NS 0f' 'Tal/RSE I C 00H55 llllllll" Inventor: Earl E.Libmarl,

His Attorneg.

Patented Nov. 22, 1938 Y 2,137,847

UNITED STATES PATENT oFFlcE STERING MOVING CRAFT Earl E. Libman,Schenectady, N. Y., assigner to General Electric Company, a corporationof New York Application May 1s, 193s, serial No. so,1oo 11 claims. (c1.25o-11) My invention relates to moving craft, such as Referring to thedrawing, Fig. 1 is a, diagram air and water craft, and particularly tothe navlshowing one relative arrangement of the course, gation of suchcraft on a predetermined straight the sources of radiant energy and thecraft; Fig. course. 2 is a diagram of a form of apparatus which may 5 Inthe Becker Patent 1,958,259, May 8, 1934, be employed constantly toindicate whether or 5 there is disclosed a system for steering movingnot the craft is on the course, to steer the craft craft on a straightcourse by the use of radio automatically to keep it on the course and toreceiving apparatus carried by the craft. In that indicate the distancetravelled by the craft and patent the radio transmitter to whose wavesthe the speed thereof.

receiving apparatus responds must be located In Fig. 1 I haverepresented the craft, such as 10 on the line of the course. One objectof my an airplane, at l which it is desired to have travel invention isto provide an improved system of on the straight course represented bythe line steering a craft on a straight course by the use D, which linemakes the angle J with the magof radiant energy, such as radio waves,which netic north, the direction of the wind being repmay be transmittedto the craft from points resented by an arrow. At the points A and B i5which are not located on the line of the course. which in the presentcase are shown located on Another object of my invention is to provideopposite sides of the cours-e D are two sources of means cooperating insaid system for measurradiant energy, such for example as radio transingthe distance traveled by the craft and the mitters operating ondifferent frequencies. These speed thereof. transmitters are representeddiagrammatically 20 In accordance with my invention I employ a at 2 and3 respectively. The line ll connecting plurality of sources of radiantenergy which are the two transmitters intersects the course D at locatedlaterally of the course that is on the the point o and makes an anglewith the course same or on opposite sides thereof and I provide D whichis known and which is represented by the craft with suitable radiantenergy receiving C. The distances between the points A and B oc- 25apparatus therefor including directive receptors cupied by thetransmitters and the course as each arranged to be oriented with respectto one measured on the connecting line 4 are known and of said sourcesto receive the energy therefrom. are represented respectively by m andn.

The line connecting two sources makes an angle If for convenience we letD represent the diswith the course which is known and the distancestance on the course from the point o to the point 3o measured on thisline between the course and Y, occupied by the craft at any instant, letA the sources also are known. As the craft travels and B representrespectively the angles at points on the course the angles formed by thecourse A and B, let m andn represent 0A and 0B reand the receptorscontinuously vary. I have spectively and let M and N representrespectively found that the relation of these angles and the the anglesat Y opposite m and n, 35

above-mentioned known quantities may be exthen pressed as an equation ofwhich one side is zero D m as long asthe craft is on the course. Byconm=m (l) tinuously solving the equation as the variable and anglesgiven by the directive receptors change,

the pilot knows if the craft has deviated from the D n (2) 40 course,and if it has he knows how to steer it sin B sin N to make propercorrection for the deviation. Since Moreover, if desired, apparatusresponsive to the A=C M (3) solution of the equation may be employed tosteer and 45 the craft automatically to maintain it on the course. Thecontinuous angular change of one of B=180(C|N) (4) the receptors forminga part of the system also Substituting in (l) is employed in eiecting ameasurement of the distance traveled by the craft and the speed D m (s)50 thereof. sin (C-M) sm M My invention will be better understood fromand in (2) the following description taken in connection with theaccompanying drawing, and its scope :TL (6) will be pointed out in theappended claims. Sm (C'i'N) sm N 55 m .i-n-lin C cos M-cos C sin M)- nmm C cos N+ cos C sm N) (8) and m(sin C cot M -cos C)=n(sin C cotN-i-cos C) (9) and sin C(m cot M-n cot N)=cos C(m+n) (10) and m cot M-ncot N also (zn-i-n) cot C-m cot M-I-n cot N=0 (12) From Equation 12above it will be seen that for every point Y on the line D the equationis satised, hence if the values of the various quantities comprising theleft hand side of this equation are substituted therein and thealgebraic sum thereof equals zero, the pilot knows that his craft is onthe course. If the craft deviates to one side of the course the leftside of the equation no longer will equal zero but will equal somepositive quantity depending upon the amount of the deviation; likewiseif the craft deviates to the other side of the course the left side ofthe equation will equal some negative quantity dependent upon the amountof the deviation. Apparatus for continuously solving Equation 12provided with means for initially setting into it the known quantitiesand for continuously feeding into it the variable quantities may beprovided with an indicator by which the pilot may know when the equationis satisfied and if not satisfied whether the craft has deviated, due todrift or other causes, to the right or to the left of the course. 'I'hecraft moreover may be provided with means controlled by sucl'i apparatusfor automatically steering it so as to cause the craft to travel on thestraight course compensating for drift or other factors which may causeit to deviate therefrom. Furthermore,

the craft may be provided with means controlled by the apparatus forindicating the distance traveled by the craft and the speed thereof.

The craft I, see Fig. 1, is provided with a plurality of radio receiverseach tuned to the frequency of one of the two transmitters 2 and 3 andeach provided with a directive receptor having means whereby it isautomatically maintained oriented with respect to the transmitter to thefrequency of which the corresponding receiver is I tuned. Thesedirective receptors are represented as antennae in the form of loops 5and 6, loop 5 being automatically maintained oriented `with respect tothe transmitter 2 at the point A in response to energy receivedtherefrom and loop 6 being automatically maintained oriented withrespect to the transmitter 3 at the point B likewise in response toenergy received from the latter transmitter. As stated above the anglebetween the course and the line AY is represented by M; likewise theangle between the course and the line BY is represented by the angle N.It will be understood that as the craft travels on its course and theangles M and N continuously change, the angles made by the loops 5 and 6also continuously change, the angles of the loops 5 and 6 serving as ameasure of the angles M and N respectively.

The craft also is provided with a compass, such for example as a magnetocompass. represented at 8 in Fig. 2 and this compass is provided withsuitable means such as that disclosed in the Becker Patent 1,991,443,February 14. 1935, for maintaining the pole pieces thereof in an eastand west position in response to the voltage produced in the armaturewhen the pole pieces are deflected from that position. This apparatus isrepresented in its entirety by the rectangle 9 which connects throughthe. gearing III and the shaft II with the pole piece mounting of thecompass. The means by which the loops 5 and 6 are maintained orientedwith respect to the transmitters 2 and 3 respectively are like thatdisclosed inthe above-mentioned patent for steering the craft and lsuchmeans are represented respectively by the rectangles I2 and I3. 'Ihesemeans, it will be understood operate directly on the shafts carrying theloops 5 and 6 in place of the cord and pulley 50 of the aforesaidpatent.

I shall now describe specifically one form of apparatus into which theabove-mentioned known fixed quantities may be initially set and intowhich the changing quantities may be continuously fed which apparatusmay be used for continuously solving Equation 12. I shall also describea form of apparatus for automatically effecting the steering of thecraft to maintain it on the course in accordance with the solving ofthat equation. In addition I shall describe a form of apparatus forindicating the distance traversed by the craft and the speed thereof,such apparatus being disclosed and claimed in the Albert L. Ruiz Patent2,066,949, January 5, 1938.

The apparatus comprises in part three similar mechanisms I, II, and IIIconstructed and connected to compute the first, second, and third termsrespectively of Equation 12. The respective mechanisms include slottedpivoted arms I6, I6', and I6" having at their outer ends the gearsegments I'l, I1', and I1" by which the arms are rotated, these gearsegments being in mesh with'pinions I8, I8', and I8". Intersecting thearms are the slotted horizontal slides I9, I9', and I9 which arearranged to move in a vertical direction only and which are threaded onthe screws 20, 20', and 20 by which they are moved. Also intersectingwith the arms are the slotted vertical slides 2|, 2|,', and 2|" whichare arranged to move in a horizontal direction only and which haveportions forming racks 22, 22', and 22" which engage the gears 23, 23',and 23". 'I'he arm and the two slides are caused to intersect at acommon point by the pin 24, 24', and It will be seen that with thisconstruction if an arm is moved to a given position and the horizontalslide ismoved to a given position, the vertical slide must assume aposition which is a function of the positions of the other two members.

'I'he known angle C is initially set into mechanism I by rotating thecrank 26 which connects through the gearing 21 with the gear I8 and withthe angle indicator 28 until the desired angle is shown by theindicator. The arm I6 of mechanism I is thereby set at the desired angleC.

The distance m is set into mechanism I by rotating the crank 30 whichconnects through the gearing 3I with the indicator 32 and through thedifferential gear 33 with the shaft 20. The resulting rotation of thescrew 20 moves the slide I9 to a position in accordance with themovement of the crank 30 as indicated by the indicator 32, Distance n isalso set into the mechanism by rotating the crank 35 whichl through thegearing 3B operates the indicator 31 and through the shaft 38, the spurgearing 39 and the differential gear 33 also turns the screw 2li in thesame direction as before so as to move the slide I9 an additional amountin accordance with the distance n as indicated by the indicator 31. Itwill be readily seenA that since the position of the arm I6 representsthe angle C and the position of the slide I9 represents the distances mplus n, the position of the slide 2| will represent the product of mplus n and the cotangent of the angle C. Thus the resulting movement ofthe gear 23 is proportional to (m-l-n) cot C which is the first term ofEquation l2.

Referring now to mechanism 1I, the loop 5 will have been moved by theorlenting means I2 through the angle between the craft axis and the lineconnecting the craft with the point A; Through the operation of themagneto compass 8 the angle of the craft axis with respect to north isadded to the above-mentioned angle by means of the'diiferential gear 40,the sum being equal to the angle M'. By turning the crank 44 the properamount as shown by the indicator 45 the magnetic bearing of the course,namely angle J, is set into the mechanism. This angle J is subtractedfrom angle M' by the differential gear dl the difference MJ which is thesame as 160-M being transmitted to segment I1 through the shaft 42,clutch 63 and pinion I 8. Thus the angle of arm I6' is equal to 180-M.

The distance m is set into mechanism II through the shaft 41 whichthrough the gearing 48 rotates the screw 20 to move the slide I9'. Sincethe angle of the arm I6' is equal to 180-M and the position of the slideI 9 represents the distance m, the position of the slide 2 I willrepresent the product of m and the minus cotangent of M. Thus theresulting movement of the gear 23 is proportional to -m cot M which isthe second term of Equation 12.

Referring now to mechanism III, the loop 6 will have been moved by theorienting means I3 through the angle between the craft axis and the.

line connecting the craft with the point B. Through the operation of themagneto compass 8 the angle of the craft axis with respect to north issubtracted from the above-mentioned angle by means of the differentialgear 50, the difference being equal to the angle N. 'I'he magneticbearing of the course having already been set in the apparatus byturning the crank 44 the angle J is added to the angle N' by thedifferential gear 5I, the sum N'+J which is the same as 180-N beingtransmitted to segment I1" through the shaft 52, clutch 53 and pinionI8". Thus the angle of the arm I6 is equal to 180-N.

The distance n is set into mechanism III through the shaft 53 whichthrough the gearing 55 rotates the screw 20 to move the slide i9". Sincethe angle of the arm I6 is equal to 180-N and the position of the slideI9 represents the distance n, the position of the slide 2 I willrepresent the Product of n and the minus cotangent of N. Thus theresulting movement of the gear 23" is proportional to n cot N which isthe negative of the third term of Equation 12.

By means of the shaft 56 and the differential gear 51 the movement ofgear 23 of mechanism I is added to that of gear 23' of mechanism II.

Likewise by means of the shaft 58 and the differential gear 59, from thesum of the movements of gears 23 and 23' is subtracted the movement .ofgear 23 of mechanism III. The final algebraio sum is transmitted throughthe gearing 60 to the dial 6I of the course indicator having the xedpointer 62. I f the craft is on the course the zero mark of the dial 6Iwill stand opposite the pointer 62 and thus indicate to the pilot thatthe craft is traveling on the course. If on the other hand the zero markis at either side of the pointer, the pilot knows that the craft hasdeviated from the course, the direction and the amount of the deviationbeing indicated by the dial. With that information he may turn therudder to bring the craft back on the course.

The craft may be steered automatically to keep it on the course bycontrolling the rudder in accordance with the angular position of thedial 6I. The means which I have illustrated for so moving the rudder isto a certain extent like that disclosed in the above-mentioned Patent1,991,443. In the present case the rudder 65 is connected by the cables66 with the gear 61 which is arranged to be moved in one direction orthe other from the mldposition illustrated by the reversible motor 68.The direction of rotation of this motor is controlled by the relay 69having the two windings 10 and 1I which are connected to be energized bythe battery 12 under the control of the discharge devices 13 and 14respectively. These devices in turn are controlled by the polarizedrelay 'I5 in a manner similar to that of the polarized relay 20' anddischarge devices 2I and 22 of the above-mentioned patent. The windingof the polarized relay 15 is arranged to be energized by current in onedirection or the other in accordance with the position of the contact 16secured to the scale 6I and arranged to move over the resistor 11. Thisresistor has its ends connected with the ends of a similar resistor 18and with the ends of the battery 19. The contact 80 carried by the gear61 and connected with the Winding of the polarized relay engages theresistor 78. By this arrangement it will be seen that as long as thecraft is on the course no current is supplied to the polarized relay 15.If, however, the course indicator shows a deviation of the craft to oneside the movement of the contact 16 supplies current in a direction toenergize relay 15 which through one or the other of the discharge tubesenergizes the relay 69 in a direction to cause the motor to turn thegear 61 so as to change the position of the rudder to correct thedeviation. The rheostat 18 and contact 80 constitute a follow uparrangement whereby the operation of the motor 68 operates to turn thecraft through successive increments until it has reached the nalposition in the same manner and for the same purpose as described in theaforementioned patent. By means of the apparatus thus described thecraft may be steered automatically in response to the initial settinginto the apparatus of the known quantities and the continued feedinginto the apparatus of the changing quantities so that the craft will bekept on the predetermined course regardless of the eifect of side winds,etc.

Equation '7 obviously may be written D=m sin (C-M) csc M (13) I shallnow describe apparatus operated by the above-described apparatus bywhich the distance traveled by the craft and the speed thereof may beindicated. Mechanism designated IV comv the course.

prises the gear mounted on the pin 88 and having a slot 81 thereinforming a cosecant cam. This gear is connected through the shaft 88 andgears thereon with the crank 28 associated with the indicator of angle Cwhereby when angle C is set into the apparatus the gear and cosecant camis rotated through an angle equal to C. Mounted concentrically with thegear 85 is the outer gear 89 which has the slotted radial arm 90. Thisgear 89 is rotated in the same direction as the inner gear through anangle equal to the angle C minus the angle M by means of thedifferential gear 9| since by this differential gear and the spurgearing 92 the movement of shaft 42 is subtracted from that of shaft 88.This differential movement is transmitted through the gearing 93 to theouter gear 89. The relative movement between the inner and outer gearsis C- (C-M) which equals M. Arranged for vertical movement between twosuitable guide surfaces is the slotted horizontal bar 95 and this bar,the arm and the face of the cosecant cam are caused to intersect at acommon point by the pin 86. Inasmuch as the relative movement betweengears 85 and 89 is proportional to angle M the distance between pins 96and 86 is equal to the cosecant of M. Also since the gear 89 has beenmoved through angle C-M the vertical displacement of the pin 96 andhence of the bar is equal to sin (C-M) csc M.

Bar 95 being common to mechanisms IV and V, the vertical movement ofthis bar is communicated to mechanism V. In this mechanism the slottedlink 98 is pivotedto the fixed pivot 99 adjacent one end and at theopposite end is pivoted to the nut |00 which is threaded on the screw|0.|. This screw connects through the gearing |02 with the screw 20 ofmechanism II. By this means the distance m is transmitted to the upperend of the link 98. The slide |03 which is similar to slide 2|,intersects the bar 95 and the link 98, the pin |04 causing the threemembers to intersect at a common point. By the mechanism V the verticaldisplacement of the bar 95 is combined with the quantity m whereby thehorizontal displacement of the slide |03 is equal to m sin (C-M) csc Mwhich according to Equation 13 equals the distance traversed by thecraft. Movement of the slide |03 may be communicated through gearingsuch as |05 to the odometer |06 which if desired may be calibrated toread in miles.

Inasmuch as the loops 5 and 6 do not necessarily follow the changingpositions of the transmitters 2 and 3 to which they are responsive withsteady movements but may follow them rather by series of smallincrements, the movement of the slide |03 accordingly may beintermittent. The average rate of movement of the slide |03 is a measureof the speed of the craft and in order that I may employ a speedometerof a common form, such as for example as that shown at |01, forindicating the speed of the craft suitable means are provided forreducing the intermittent motion to a steady movement. Such means I haverepresented as comprising a well known form ofA overrunning clutch |08between which and the speedometer is the flywheel |09.

If the course to be traveled is such that it passes through one of thetransmitters, for example, the transmitter 3 at the point B, then theangle N will be zero as long as the craft is on In this case for courseindication and automatic steering transmitter 2 and the receiverincluding loop 5 are not necessary, hence clutches I3 and 88 should bedisconnected and quantity n should be set at zero. The clutch ||2 willbe closed thereby establishing a direct connection between the shaft 52and the indicator through the shaft ||3 and gearing Ill, the mechanismsl1 and III now being inoperative. Thus any change in angle of loop 8resulting from a deviation of the craft from the course will beindicated by the indicator 6| as before. The distance traveled and thespeed of the craft are obtained by mechanisms IV and V as a result ofthe changing angle M in the manner already described above.

While for convenlencein this disclosure I have shown and referred toradio transmitters, radio receivers, directive antennae in the form ofloops and a magnetic compass, it will be understood that this is merelyfor the purpose of illustration and that I do not Wish the scope of myinvention to be confined to such elements. I may wish to employ aradiant energy transmitter which will emit extremely short waves havingthe characteristics of light waves, infra red waves, heat waves or lightwaves. I may4 also employ receiving means including photoelectricdevices or thermoelectric devices. Moreover I may employ directiveantennae of other types and may employ a compass of any other well knownand suitable type. In the drawing I have not attempted to show thevarious parts of the apparatus in their true relative proportions norhave I attempted in all cases to show the gears arranged for rotation inthe proper direction or having the proper gear ratio.

I have chosen the particular embodiment described above as illustrativeof my invention and it will be apparent that various modifications maybe made without departing from the spirit and scope of my inventionwhich modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A system for steering a moving craft on a straight course comprisingmeans for producing radiant energy at a plurality of points positionedlaterally of said course, the angle between the course and the lineconnecting the points and the distances of the points from the coursemeasured on the line being known, means on said craft for receiving saidenergy including a plurality of receptors each arranged to be maintainedoriented with respect to one of said points, means for setting into saidsystem quantities corresponding with said known angle and distances `andmeans operative in response to said quantities and to the angles betweenthe course and said receptors to indicate Whether or not the craft is onthe course.

2. A system for steering a moving craft on a straight course comprisingmeans for transmitting radiant energy from a plurality of pointspositioned laterally of said course, the angle between the course andthe line connecting the points and the distances of the points from thecourse measured on the line being known, means on said craft forreceiving said energy including a plurality of receptors each providedwith means for maintaining it oriented with respect to one of saidpoints, separate means operative to set into said system quantitiescorresponding with said known angle and each of said distances and meansoperative in response to said quantities and to the angles between thecourse and said receptors to indicate whether or not the craft is on thecourse.

3. A system for steering a moving craft on a straight course comprisingmeans for producing radiant energy at a plurality of points positionedlaterally of said course, the distances between the points and thecoursemeasured along the line connecting the points being equal to m and n andthe angle between said line and the course being equal to C, means onsaid craft for receiving said energy including a plurality of receptorseach arranged to be maintained oriented with respect to one of saidpoints and making angles with the course equal respectively to M and N,the relation of said distances and said angles when the craft is on thecourse being expressed by the equation:

(m-i-n) cot C-m cot M-i-n cot N=0,

and means responsive to said known angle and distances and to the anglesmade by said receptors for indicating whether or not the equation issatised.

4. A system for steering a moving craft on a straight course comprisingmeans for producing radiant energy at a plurality of points positionedlaterally of said course, the distances between the points and thecourse measured along the line connecting the points being equal to mand n and the angle between said line and the course being equal to C,means on said craft for receiving said energy including a plurality ofreceptors each arranged to be maintained oriented with respect to one ofsaid points and making angles with the course equal respectively to Mand N, the relation of said distances and said angles when the craft ison the course being expressed by the equation:

(m-l-n) cot C-m cot M-i-n coi'l N=0,

means responsive to said known angle and distances and to the positionof said receptors for continuously solving said equation and anapparatus responsive to the satisfying of said equation.

5. A system for guiding a moving craft in a straight course comprising aplurality of radio transmitters operating at dierent frequencies andspaced laterally of said course, the distances between said transmittersand said course measured along the line connecting the transmittersbeing equal to m and n and the angle between said line and said coursebeing equal to C, a plurality of radio receivers on said craft, eachreceiver being provided with a directive receptor having means forautomatically maintaining it oriented with respect to one of saidtransmitters in response to energy received therefrom, the receptorsmaking angles with the course equal to M and N and the relation of saiddistances and said angles when the craft is on said course beingexpressed by the equation:

(m4-n) cot C-m cot M-l-n cot N=0,

means responsive to said known angle and distances and to4 the positionof said receptors for continuously solving said equation and meansindicating when said equation is satisfied.

6. A system for steering a moving craft in a straight course comprisinga plurality of radio transmitters operating at different frequencies andspaced laterally of said course, the angle between said course and theline joining said transmitters being known and equal to C, the distancesof said transmitters from the course measured on said line being knownand equal to m and n respectively, a plurality of radio receivers onsaid craft, each receiver being tuned to the frequency of one of saidtransmitters and provided with a directive antenna having means bywhichit may be maintained oriented with respect to the transmitter towhich it is tuned in accordance with the energy received therefrom, thechanging angles between the course and the respective antenna beingequal to M and N, the relation of said quantities when the craft is onsaid course being expressed by the equation:

(m4-n) cot C-m cot M-l-n cot N=0,

a computing mechanism provided with a dial and carried by the craft forsolving said equation, means for setting said known quantities into saidmechanism and means for continuously feeding said changing angles intosaid mechanism, said dial indicating whether or not said equation issatisfied.

'7. A system for steering a. moving craft in a straight coursecomprising a plurality of radio transmitters operating at differentfrequencies and spaced laterally of said course, the angle between saidcourse and the line joining said transmitters being known and equal toC, the distances of said transmitters from the course measured on saidline being known and equal to m and n respectively, a plurality of radioreceivers on said craft, each receiver being tuned to the frequency ofone of said transmitters and provided with a directive antenna havingmeans by which it may be maintained oriented with respect to thetransmitter to which it is tuned in accordance with the energy receivedtherefrom, the changing angles between the course and the respectiveantennae being equal to M and N', the relation of said quantities whenthe craft is on said course being expressed by the equation:

(m-i-n) cot C--m cot M-l-n cot N=0,

for setting said known quantities into said mech anism, means forcontinuously feeding said changing angles into said mechanism andsteering mechanism for said craft responsive to the output of saidcomputing mechanism.

8. A system for steering a moving craft on a straight course comprisingmeans for producing radiant energy at a plurality of points positionedlaterally of said course, the angle between the course and the lineconnecting the points and the distances of the points from the coursemeasured on the line being known, means on said craft for receiving saidenergy including a plurality of receptors each arranged to be maintainedoriented with respect to one of said points, means for setting into saidsystem quantities corresponding with said known angle and distances,means operative in response to said quantities and to the angles betweenthe course and said receptors to indicate whether or not the craft is onthe course and means responsive to the angle between the course and oneof said receptors for indicating the distance traveled.

9. A system for steering a moving craft on a straight course comprisingmeans for producing radiant energy at a plurality of points positionedlaterally of said course, the angle between the course and the lineconnecting the points and dii- ' tained oriented with respect to one ofsaid points.

means for setting into said lsystem quantities corresponding with saidknown angle and distances, means operative in response to saidquantities and to the angles between the course and said receptors toindicate whether or not the craft is on the course, and means responsiveto the changing angle between the course and one of said receptors forindicating the speed of the craft.

10. A system for steering a moving craft on a straight course comprisingmeans for producing radiant energy at a plurality of points positionedlaterally of said course, the angle between the course and the lineconnecting the points and the distances' of the points from the coursemeasured on the line being known, means on said craft for receiving saidenergy including a plurality of receptors each arranged to be maintainedoriented with respect to one of said points, means for setting into saidsystem quantities corresponding with said known angle and distances,means operative in response to said quantities and to the angles betweenthe course and said receptors to steer the craft to keep it on thecourse, and means responsive to the changing angle between the courseand one of said receptors for indicating the distance traveled.

11. A system for steering a moving craft on a straight course comprisingmeans for producing radiant energy at a plurality of points positionedlaterally of said course, the angle between the course and the lineconnecting the points and the distances oi' the points from the coursemeasured on the line being known, means on said craft for receiving saidenergy including a plurality of receptors each arranged to be maintainedoriented with respect to one of said points, means for setting into saidsystem quantities oorresponding ,with said known angle and distances,means operative in response to said quantities and to the angles betweenthe course and said receptors to steer the craft to keep it on thecourse, and means responsive to the changing angle between the courseand one of said receptors for indicating the speed of the craft.

EARL E. LIBMAN.

